Multi-tap distribution apparatus

ABSTRACT

There is provided a distribution apparatus in which transmission losses at the connections between ends of transmission lines and input and output terminals of a mother board are reduced. These ends of the transmission lines are positioned on resin support pieces. A resin support piece (19) is provided at a dead end of each groove (6a) formed in a housing (1). An end portion of a metal rod (6b) is placed on the support piece (19). The end portion of the rod (6b) has a threaded hole (20) formed therethrough. The mother board (11) is provided with two first lands (22,23) each surrounding a screw hole (21). A screw (22a) is tightened in each threaded hole (20), which is part of a main line connection terminal (5b), thereby bringing the head of the screw (22a) into firm contact with the first land (22) and establishing an electrical connection between the first land (22) and the conductive rod (6b). Provided outside each of the first land (22) is a circular and concentric second land (23) with a portion cut out of it. The second land (23) is insulated from the first land (22) and electrically connected to the housing (1) via contact pieces (23a) projected from the rear surface of the mother board (11).

FIELD OF THE ART

The present invention relates to a multi-tap distribution apparatus.More particularly, the present invention relates to a multi-tapdistribution apparatus which is suitable for use with CATV cables.

BACKGROUND ART

Distribution apparatus for being interposed in CATV transmission cablescome in different types due to the needs to provide input and outputcable connecting portions in different positions and also to providevarious numbers of taps. To meet these needs, multi-tap distributionapparatuses for general purpose use have been proposed whose internalmechanisms are composed of a plurality of modules. In one type of suchgeneral-purpose distribution apparatuses, a mother board with a currenttransmission circuit and a branch circuit board are designed in modulesthat can be assembled in different ways to suit particular applications.

CATV transmission cables carry not only television signals, controlsignals, and other high-frequency signals but also currents foroperating main line amplifiers. For this reason, the above-mentionedtype of distribution apparatuses are designed to transmit currentstherethrough. Currents should not be carried through the branch circuitor the distribution circuit of this type of apparatuses. To avoid this,these distributors have a dedicated circuit provided in a mother boardespecially for current transmission and connect the input and outputcable connecting portions via the dedicated circuit. Generally, theseapparatuses employ an insertion type connecting structure to connect themother board with the transmission cables, which are directly coupled tothe input and output cable connecting portions.

Although only currents of low amperage are passed to each tap in thistype of apparatuses, the cable connecting portions carry the samemaximum currents as the main line does. Therefore, the transmissionlosses between the input and output cable connecting portions must bereduced and any adverse effect on the characteristics of theelectromagnetic waves must be also minimized.

However, the aforementioned insertion type connecting structure causesnot only transmission losses easily but also over-heating if a currentof high amperage is carried therethrough, so that the heat may affectthe characteristics of the circuits mounted on the mother board.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a distributionapparatus in which transmission losses at the connections between endsof transmission lines and input and output terminals of a mother boardare reduced.

It is another object of this invention to provide transmission lines forelectrically connecting the input and output terminals of a mother boardto cable connecting portions provided on sides of a case comprising themother board.

It is a further object of this invention to provide lands aroundthrough-holes in the mother board into which electrically conductivescrews are inserted to establish electrical connections between thetransmission lines and the input and output terminals of the motherboard.

These and other objects are further accomplished by a distributionapparatus for being interposed in a transmission cable, the distributionapparatus comprising, a built-in mother board disposed in theapproximate center of a case, the mother board including, a branchcircuit for distributing as output signals high-frequency signalsreceived at an input terminal of the mother board, and a currenttransmission circuit for allowing currents to be transmitted between theinput terminal and an output terminal of the mother board, transmissionlines for electrically connecting the input and output terminals of themother board to cable connecting portions provided on sides of the case,the transmission lines each having a center conductor with a threadedhole formed in one end thereof, each of the central conductors of eachof the transmission lines is disposed in a groove formed in an innerwall of the case without being in contact with the inner wall, and astructure for connecting each of the central conductors to the motherboard is assembled at a dead end of the groove, and lands providedaround through-holes which are formed in the mother board and throughwhich electrically conductive screws are inserted, wherein the screwsare tightened into the threaded holes through the through-holes so thatelectrical connections are established between the transmission linesand the input and output terminals of the mother board via the screws.At least three cable connecting portions are provided so that two cableconnecting portions are selectable from the at least three cableconnecting portions for connection to the mother board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a multi-tap distributionapparatus of an embodiment of the present invention.

FIG. 2 shows a plan view of the components of the multi-tap distributionapparatus.

FIG. 3 shows a circuit diagram of the components of the multi-tapdistribution apparatus.

FIGS. 4A and 4B show the transmission line of the embodiment.

FIG. 5 is a cross sectional view of the transmission line taken on lineA--A of FIGS. 4B.

FIG. 6 shows an alternate transmission line of the embodiment.

FIG. 7 is a cross sectional view of the transmission line taken on lineB--B of FIGS. 4B.

FIG. 8 shows the main line connection terminal of the embodiment.

FIG. 9 is a cross sectional view illustrating how the main lineconnection terminal is connected to the mother board.

FIG. 10 shows the current passage contact of the embodiment.

FIGS. 11A and 11B shows the current passage contact in two states.

FIGS. 12A, 12B, and 12C show different pairs of cable connectingportions for use as terminals.

BEST MODE FOR CARRYING OUT THE INVENTION

A multi-tap distribution apparatus embodying the present invention willbe explained with reference to the attached drawings. The multi-tapdistribution apparatus of the embodiment is provided with three cableconnecting portions so as to be used as either an aerial type orpedestal type device. Also, the number of taps can be changed in thedistribution apparatus of this embodiment.

Referring to FIGS. 1 to 3, reference numeral 1 designates a box-shapedhousing made of die-cast aluminum with one side open. The housing 1 (oneof the two components forming the entire case) is provided with onecable connecting portion 2 on one end surface and two other cableconnecting portions 3 and 4 on the opposite end surface. Each of thecable connecting portions 2, 3, and 4 is disposed on a corner of thehousing 1. Cable connector insertion holes 2a, 3a, and 4a are providedin the end surfaces while three screw access holes 2c, 3c, and 4c areprovided in the longitudinal sides of the housing 1. The screw accessholes 2c, 3c, and 4c are normally closed with blind bolts 2b, 3b, and4b.

The housing 1 has in its center a circuit mounting area 5 on which threemain line connection terminals 5a, 5b, and 5c are provided. The upperterminals 5a and 5b are located above, and on the right and left sidesof, the center P of the housing 1 while the terminal 5c is locateddirectly under the right terminal 5b. The terminals 5a, 5b, and 5c areconnected to the cable connecting portions 2, 3, and 4, respectively,via transmission lines 6.

Referring to FIGS. 4A and 4B, each transmission line 6 has a coaxialstructure formed on the inner wall of the housing 1. The transmissionline 6 includes a brass or copper conductive rod 6b disposed as thecentral conductor in a groove 6a without being in contact with the innerwall of the groove 6a. The groove 6a has a semi-circular cross sectionand a shield wall erected on each side.

The transmission line 6 further includes a dielectric block 7 which ispenetrated by the conductive rod 6b and mounted in the groove 6a. Thedielectric block 7 has an outer shape that fits in the groove 6a andoccupies part of the groove 6a so as to be slidable in the longitudinaldirection of the groove 6a.

Being formed on the inner wall of the case in this manner, thetransmission line 6 offers the following advantages. The thickness ofthe conductive rod 6b can be freely changed. Moreover, referring to FIG.5 showing a cross section taken on line A--A, each transmission line hasa layer S of air between the conductive rod 6b and the inner wall of thegroove 6a, which serves as the outer conductor. This structure causesonly a small transmission loss so that the transmission line is capableof coping with currents of high amperes. Furthermore, the structureallows adjustment of the high-frequency characteristics of thetransmission line by moving the dielectric block 7 along the groove.

The preferred material of the dielectric block 7 is Jurakon (a brandname; manufactured by Polyplastics Corporation). Alternatively, theblock may be made of some other synthetic resin with similar electricalcharacteristics. Depending on the application, the dielectric block 7may be fixed in the groove 6a so as not to be slidable. Furthermore, asshown in FIG. 6, a plurality (for example, two as shown) of thedielectric blocks may be fixed in each groove 6a. As illustrated, eachof the blocks 7 may be divided into two sections with the two uppersections connected by an arm 7a, so that the upper sections can beeasily mounted in the groove by securing the arm 7a to the housing 1with a screw.

Also, a split tube 8 with a slit is secured to one end of the conductiverod 6b. The split tube 8 is gripped and supported by a pair of gripblocks 9 in the cable connecting portion 2 (3, 4). The grip blocks 9 areconnected by a hinge. A tube support groove 9a is formed in the splitsurface of each block. Furthermore, a block securing recess 9b which isformed integrally with the groove 6a is provided in the cable connectingposition on the inner surface of the housing 1.

For assembly, as shown in FIG. 7 which illustrates a cross section takenon line B--B, the split tube 8 is gripped in the support grooves 9a byfitting the two grip blocks 9 together. Then, the blocks 9 arepositioned in the block securing recess 9b and secured by tightening ascrew 9c at a side.

Then, a connector 10 attached to one end of a transmission cable isfitted into the cable insertion hole 2a (3a, 4a) by inserting a pin 10aof the connector 10 into the split tube 8. Finally, the screw 9c istightened to firmly and securely connect the pin 10a to the split tube 8between the grip blocks 9.

A metal abutment plate 8a is mounted on one of the grip blocks 9 wherethe screw abuts against the block to prevent cracking or deformation ofthe grip block. In addition, the abutment plate 8a allows the pressureof the screw 9c to be distributed over the entire length of the gripblock 9. Also, the screw 9c can be tightened from the outside throughthe screw access hole upon removing the blind bolt 3b (2b, 4b).

Reference numeral 11 is a mother board having a pair of transmissionterminals 12 on its rear face and a pair of relay terminals 13 on itsfront face. The transmission terminals 12 are spaced apart so as tocorrespond with the main line connection terminals 5a and 5b (or 5b and5c). Each of the transmission terminals 12 is connected to a relayterminal 13 via a high-frequency passing circuit 14 with a capacitor 14ainterposed therein. The circuits 14 allow high-frequency signals to passtherethrough. The two transmission terminals 12 are connected to eachother by a current transmission circuit 15 with a coil 15a interposedtherein. The current transmission circuit 15 is also protected with acover.

Also, the housing 1 has a plurality of guide pins 16 projected therefromwhile the mother board 11 has a plurality of guide holes 17 formedtherein corresponding to the guide pins 16. The mother board 11 ismounted in the housing 1 by inserting the guide pins 16 into the guideholes 17. In this way, the transmission terminals 12 are easily alignedand brought into contact with, for example, the main line connectionterminals 5a and 5b, although these terminals are not visible behind themother board 11 during mounting. Then, the mother board 11 is secured tothe housing 1 with a pair of screws 18.

Also, the mother board 11 has a pair of screws tightened through thetransmission terminals 12 to firmly secure the terminals 12 to the mainline connection terminals 5b (5a, 5c).

Referring to FIGS. 4A and 4B, each of the main line connection terminals5a, 5b, and 5c includes a resin support piece 19 provided at a dead endof the groove 6a and an end portion of the conductive rod 6b placed onthe support piece 19. The end portion of the rod 6b has a threaded hole20 formed therethrough. As shown in FIG. 8, the transmission terminal 12is provided with a first land 22 surrounding a screw hole 21 in themother board 11. The conductive screw 22a, made of brass or iron forexample, is tightened in the threaded hole 20 of the main lineconnection terminal 5b, thereby bringing the head of the screw 22 intofirm contact with the first land 22a and establishing an electricalconnection between the first land 22 and the conductive rod 6b.

If the conductive rod 6b is securely supported by two dielectric blocks7 as shown in FIG. 6, the support piece 19 is optional and can beomitted from the main line connection terminal 5b (5a, 5c).

Provided outside the first land 22 is a circular and concentric secondland 23 with a portion cut out of it. The second land 23 is insulatedfrom the first land 22 and electrically connected to the housing 1 viacontact pieces 23a projected from the rear surface of the mother board11. Thus, the main line connection terminal 5b (5a, 5c) is coaxiallyconnected to the transmission terminal 12 (see FIG. 9).

Also, the mother board 11 has a pair of engaging slits 14 formed thereinoutside the relay terminals 13.

Reference numeral 25 designates a box-shaped branch unit which has onone surface a pair of connection terminals 26 and 26' which correspondto the relay terminals 13 of the mother board 11. The branch unit 25 hason the opposite surface a branch terminal 27. The connection terminals26 and 26' and the branch terminal 27 are connected to a built-in branchcircuit. With the connection terminal 26 serving as the input terminaland the connection terminal 26' serving as the output terminal, thebranch unit 25 can convey high-frequency signals in a predetermineddirection. It also has on both ends thereof two engaging claws 28projected toward the surface where the connection terminals 26 and 26'are located. When the branch unit 25 is mounted on the mother board 11by engaging the claws 28 with the slits 24, the connection terminals 26and 26' are brought into contact with the relay terminals 13.

The branch unit 25 on the mother board 11 may be mounted by some othermethod. For example, the engaging claws formed on the branch unit may bereplaced with guide lugs which are inserted into the slits formed in themother board. Furthermore, screws or clips may be employed as the meansof mounting the branch unit on the mother board.

The mother board 11 is provided with a push switch 29. When the branchunit 25 is mounted on the mother board 11, the outer surface of thebranch unit 25 presses against and turns off the switch 29. When thebranch unit 25 is detached from the board mother 6, the push switch 29is released from the pressure of the unit 25 and turned on, thusshort-circuiting the relay terminals 13 and allowing passage ofhigh-frequency signals between the transmission terminals 12.

Moreover, the current transmission circuit 15 of the mother board 11ensures that currents and high-frequency signals flow between thetransmission terminals 12 whether or not the branch unit 25 is mountedon the mother board 11.

Reference numeral 30 is a tap board mounted on the inner surface of amain body 31. Together with the housing 1, the main body 31 constitutesthe entire case of the distribution apparatus. The tap board 30 includesa distributing circuit and four external taps 32 exposed on the outersurface of the main body 31. The external taps 32 serve as distributionoutput terminals. The tap board 30 also has on its inner surface aninput terminal 33 corresponding to the branch terminal 27 of the branchunit 25. Additionally, the housing 1 is provided with a current passagecontact 34 which is connected to the cable connecting portion 2 whilethe main body 31 is provided with another current passage contact 35which is connected to the distributing circuit. Therefore, currents canbe transmitted through these two contacts. The current passage contact34 is connected to the external taps 32 via a current passage network 36provided in the tap board 30. By fitting the main body 31 on the housing1, the branch terminal 27 is brought into contact with the inputterminal 33. At the same time, an electrical contact is also establishedbetween the current passage contacts 34 and 35, thereby forming aseparate current passing route from the high-frequency passing route.

As shown in FIG. 10, the current passage contact 35 is of a pin typebiased toward the tip thereof by a coil spring 35a. The current passagecontact 35 is welded at its bottom end to the print-circuit board or thetap board 30 so as to be erected on the tap board. The contact, ifshifted off the insertion-type current passage contact 34, compressesthe coil spring 35a and moves backward, with its tip abutting on aprotective plate 41 (explained in further detail below) (see FIG. 11A).However, when the housing 1 is moved with respect to the main body 31,the current passage contact 35 also moves smoothly on the protectiveplate 41. When the two contacts are aligned with each other, the contact35 are projected forward by the biasing force of the coil spring 35a toreestablish an electrical contact (see FIG. 11B).

A positive thermistor 37 (model name: Polyswitch RXE065; manufactured byReikem Corporation) is interposed between the contact 35 and eachdistribution output terminal via a connector 38 in the current passagenetwork 36. The positive thermistors 37 can be easily coupled to anddetached with a single motion from the connectors 38 (model name: VHseries connector; manufactured by Nippon Solderless TerminalCorporation).

The right and the left fitting ends of the housing 1 and the main body31 have different shapes so that the housing and the body can beassembled in only one way. Assembly is possible only when a lug 39projected from the housing 1 is inserted into a groove 40 formed in themain body 31. In this way, whenever the housing and the body areassembled, left-to-right inverted assembly is prevented while a secureelectrical contact is established between the current passage contacts34 and 35.

The current passage contact 34 is connected to the split tube of thecable connecting portion 3 via a current passage cable 34a. Normally,the upper surface of the current passage contact 34 is covered with theprotective plate 41 which has a terminal insertion hole 41a to preventthe worker from accidentally touching the contact 34 and receiving anelectric shock while at work.

The aforementioned protective plate 41 is made of a highly insulating,slippery resin such as ABZ resin so that the tip of the current passagecontact 35 can be smoothly shifted on the plate 41.

As shown in FIG. 12A, the multi-tap distribution apparatus can be usedas an aerial type device if the branch unit 25 is mounted on the motherboard 11 with the terminal 26 on the same side as the cable connectingportion 2 and the terminal 26' on the same side as the cable connectingportion 3. In this case, the cable connecting portion 2 is used as theinput terminal while the cable connecting portion 3 is used as theoutput terminal.

The positions of the input and output terminals can be easily reversedby detaching and horizontally rotating the branch unit 25 one hundredand eighty (180) degrees and mounting it back on the mother board 11(see FIG. 12B).

To use the multi-tap distribution apparatus as a pedestal type device,the mother board 11 is detached and rotated 90 degrees in clockwisedirection as shown in FIG. 12C, so that the connection terminals 26 and26' are connected with the main line connection terminals 5b and 5c viathe transmission terminals 12. In this application, the cable connectingportion 3 serves as the input terminal and the cable connecting portion4 as the output terminal. The positions of the input and outputterminals can be easily reversed as in the aerial type application: bydetaching and rotating the branch unit 25 one hundred and eighty degreesand mounting it back on the mother board 11 (this position is notshown).

To change the number of branches (secondary cables), the main body 31,the tap board 30, and the branch unit 25 are replaced with a differentmain body incorporating a tap board having a desired number of taps anda different branch unit.

To perform such a replacement, the branch unit 25 can be easily detachedby disengaging the claws 28 from the slits 24. Upon detachment of thebranch unit 25, the switch 29 is turned on, thus short-circuiting thetransmission terminals 12 and maintaining high-frequency signaltransmission between the cable connecting portions. Accordingly, thehigh-frequency signal transmission remains uninterrupted while thebranch unit 25 is replaced.

In this embodiment, different cable connecting portions can be selectedfor use as the input and output terminals by rotating the mother board90 degrees. Also, the number of taps can be increased or decreased byreplacing the branch unit and the main body. Not only does thisconstruction improve the operability of the multi-tap distributionapparatus, but it also allows the multi-tap distribution apparatus to beused as an aerial or pedestal type. Moreover, the multi-tap distributionapparatus offers the advantage of maintaining the check function from aremote site even when the branch unit or the main body is removed sincethe transmission of the currents and the high-frequency signals from theinput side to the output side remains uninterrupted.

If the transmission cable is used as a telephone line, telephoneconversations are not interrupted by using the current transmissioncircuit and the telephone line as the telephone uses signals in thelow-frequency range.

If a short circuit occurs on the distribution output terminal side, theresistance of the positive thermistor included in the current passagenetwork increases from tenths of an ohm to several kilo ohms, thusblocking the current flow between the cable connecting portion and thedistribution output terminal. This protects the circuits in thedistribution apparatus while preventing damage to equipment and devicesconnected to the transmission cable. This structure can be safely usedin applications where currents of 15 amperes or more are conveyed.

As explained above, the high-frequency transmission circuit (branchcircuit) is installed separately from the current passage network and apositive thermistor is connected to each distribution output terminal.Therefore, if a short circuit occurs, the current flow is interruptedonly to the concerned branch output terminal while maintainingtransmission of the television signals.

Since a positive thermistor is detachably connected to each externaltap, it is possible to leave installed the positive thermistors for theexternal taps connected to the subscribers using telephone lines forreceiving CATV services. Meanwhile, the power supply can be easilystopped to non-subscribers by removing from the connectors the positivethermistors for the external taps which are connected tonon-subscribers. Not only can this operation be simply done but also itis easy to recognize to which externals taps currents are carried.

Alternatively, the same result can be obtained by providing switches(not shown) in the current passage network and selectively turning onand off the switches instead of detaching positive thermistors asexplained above.

Furthermore, the multi-tap distribution apparatus may have only twocable connecting portions instead of three as in this embodiment.Furthermore, the number of taps may be either increased or decreased,the main body may have any number of taps.

As described above, the embodiment includes three main line connectionterminals on the inner surface of the housing. Two of the terminals arelocated above and on both sides of the center of the housing while thethird terminal is located directly under one of the upper terminals.Accordingly, the pair of main line connection terminals of the motherboard to be connected with the transmission terminals can be selected byrotating the mother board. Instead of this construction, equally spacedpairs of main line connection terminals may be arranged on the housingso that the transmission terminals are connected to any desired pair ofmain line connection terminals by shifting the mother board. However,the present invention is applicable to the types of models in which mainline connection terminals cannot be selected for connection or thenumber of external taps cannot be changed.

To change the mounting position of the mother board, all that isrequired is to remove screws and tighten them after the mother board isshifted to a new position. Since the screws, when tightened, firmlyconnects the end portions of the metal rods or central conductors of thetransmission lines to the transmission terminals of the mother board,which serves as the input and output terminals of the mother board. Thepossibility of over-heating is effectively prevented by this structure.

Effect of the Invention

According to the invention, the input and output terminals of the motherboard are securely connected to ends of the transmission lines withscrews, with each of the line ends positioned on a support piece. Thisconnecting structure provides a sufficient capacity to carry largecurrents between the cable connecting portions, thereby reducing thetransmission losses between the cable connecting portions coupled toeach other via the current transmission circuit as well as preventingover-heating and thus the adverse effect on the characteristics of thecircuit of the mother board.

Furthermore, as a pair of cable connecting portions are selectable froma plurality of portions, a single distribution apparatus can be used aseither an aerial or pedestal type apparatus.

Also, as each transmission line is disposed in a groove without being incontact with the inner wall of the groove, the transmission losses canbe further reduced to a very minimum.

I claim:
 1. A distribution apparatus for being interposed in atransmission cable, said distribution apparatus comprising,a built-inmother board disposed in the approximate center of a case, said motherboard including, a branch circuit for distributing as output signalshigh-frequency signals received at an input terminal of said motherboard, and a current transmission circuit for allowing currents to betransmitted between said input terminal and an output terminal of saidmother board, transmission lines for electrically connecting said inputand output terminals of said mother board to cable connecting portionsprovided on sides of said case, said transmission lines each having acenter conductor with a threaded hole formed in one end thereof, each ofthe central conductors of each of said transmission lines is disposed ina groove formed in an inner wall of said case without being in contactwith said inner wall, and a structure for connecting each of saidcentral conductors to said mother board is assembled at a dead end ofthe groove, and lands provided around through-holes which are formed insaid mother board and through which electrically conductive screws areinserted, wherein said screws are tightened into said threaded holesthrough said through-holes so that electrical connections areestablished between said transmission lines and said input and outputterminals of said mother board via said screws.
 2. The distributionapparatus in accordance with claim 1 wherein at least three cableconnecting portions are provided so that two cable connecting portionsare selectable from said at least three cable connecting portions forconnection to said mother board.